A technique has been conventionally known in which: cameras installed in a vehicle capture and obtain images of surroundings of the vehicle; and an amount of movement of the vehicle is obtained based on changes in the images (see Japanese Patent Application Publication No. 2008-175717, for example). Japanese Patent Application Publication No. 2008-175717 aims at obtaining the amount of movement of the vehicle accurately even if the vehicle moves slightly at slow-speed. To this end, a feature point is detected from each image; the position of the feature point is obtained; and thereby, the amount of movement of the vehicle is obtained from the direction and distance of movement (amount of movement) of the feature point.
In addition, a technique of performing a three-dimensional measurement using a laser beam projector for projecting a laser beam in a grid pattern (patterned light beam) has been known (see Japanese Patent Application Publication No. 2007-278951, for example). According to Japanese Patent Application Publication No. 2007-278951, an image of an area of the projected patterned light beam is captured with a camera; the patterned light beam is extracted from the captured image; and a behavior of the vehicle is obtained from the position of the patterned light beam.
In an outdoor environment, however, when a patterned light beam is projected onto a road surface as described in Japanese Patent Application Publication No. 2007-278951, the patterned light beam is influenced by ambient light. For this reason, it is difficult to detect the patterned light beam projected onto the road surface.